The present invention relates to a pyrotechnic actuator according to the preamble of claim 1.
A generic actuator is known from U.S. Pat. No. 4,091,621. The U.S. Pat. No. 4,091,621 shows a pyrotechnic actuator, in the case of which an explosive is electrically ignitable, whereby the gas arising moves a piston. A lock prevents the piston returning from its terminal position to its initial position. In this case the locking action is provided by a c-shaped clamp ring held in a circumferential groove of the piston, which in the compressed, that is to say spring-loaded condition lies in the cylinder with the piston. As soon as the piston is moved out of the cylinder by the developing gas, the tensioned, c-shaped ring can de-tension, as a result of which its radius becomes greater than the inner radius of the cylinder. Also in the de-tensioned condition the c-shaped ring remains in the groove of the piston. If the piston tries to move back again to its initial position, the c-shaped ring strikes the head of the cylinder and prevents the piston from entering the cylinder.
A disadvantage with this embodiment according to U.S. Pat. No. 4,091,621 is that the piston is only retained in its position by friction. This friction stops when the c-shaped ring has left the cylinder. Secure anchoring of the piston in its initial position is however not assured by friction. If it is further considered that such systems must be ready to operate but are not used over a long period, the locking requirement cannot be met by means of friction. This is especially therefore the case, since there is no guarantee that the tension in the c-shaped ring is maintained for several years by the metal. If for example the pyrotechnic actuator is used in a vehicle, this must still be completely functional after 10 or 20 years. This is only guaranteed if the piston always remains in its initial position.
The aim of the present invention is therefore to provide a pyrotechnic actuator, in which the piston is securely retained in its initial position. This aim is achieved according to the invention by a pyrotechnic actuator with the features of claim 1. Further advantageous embodiments of the object of the invention are clear from the features of the sub-claims.
Through the use of a snap-in element and/or a sprung retaining element the piston is advantageously retained in the initial position. Corresponding elements can for example be sprung contact studs or snap connections. The action of the elements guarantees in this case that simply by applying minimum force to the piston it can be moved from its initial position to the terminal position. Through the use of corresponding ratchet- or retaining elements the necessary minimum force can be pre-determined precisely. This is an important advantage compared to the known friction, which is affected by several factors and which can only be inadequately calculated. In addition the necessary minimum force for moving the piston from the initial to the terminal position does not change over time, since for example a sprung contact stud as an initial position retaining element is not stressed by force, but force is only applied on it when the piston is moved. As a result metal fatigue is prevented advantageously.
The ratchet- or retaining elements used advantageously at the same time to serve as retaining elements, which retain the piston in the terminal position after this has been reached. This means that advantageously no extra parts are required and therefore the retaining function in the initial as well as in the terminal position can be realised with few parts.
Advantageously several ratchet- or retaining elements can be provided so that the piston is prevented from going back to the initial position, not just after reaching the terminal position, but also on the way from the initial position to the terminal position it is prevented by the several ratchet or retaining elements, after passing one of the elements, from going back from this position to the initial position.
Advantageously both the ratchet as well as the retaining elements can together ensure the piston is locked. In this case all locking mechanisms, which in particular are the embodiments illustrated in the figures, can be used in combination with one another.
Advantageously the ratchet- and/or retaining elements are moulded or secured on the piston or the cylinder itself. In this case for example as snap-in or retaining elements a contact stud or bow-spring can be used, which for example interacts with a saw-tooth shaped surface structure or engages in appropriately functional cavities, so that the piston can move in relation to the cylinder each time in only one direction after overcoming a minimum force.
An especially preferred embodiment of a pyrotechnic actuator is the case if the piston has a cavity extending in the lengthwise direction of the piston, into which a stud on the housing engages as the gripping mechanism, whereby the ratchet or securing elements work together with the pin or stud fixed rigidly on the housing. The pin or stud together with the longitudinal cavity or oblong window-type aperture acts as a bearing and guide for the stud. In this case the ratchet or retaining elements are arranged on the piston itself.
If the piston is an injection moulded part, the ratchet- or retaining elements can be formed by means of a plate inserted in the piston, whereby for example the plate advantageously forms the wall of the oblong cavity or window-type aperture, so that the stud can securely slide in the oblong cavity or window-type aperture. Through the use of a suitably curved and stamped metal plate to form the inner wall as well as the ratchet or securing elements, the piston can also be reinforced, as a result of which greater forces can be applied by the piston itself to trigger a particular operation.
Through the advantageous use of an oblong cavity or window-type aperture for the interplay with a locking pin or stud, the ratchet or securing elements can be designed so that the pin or stud pivots or moves the ratchet or securing elements to the side when the piston moves from the initial position to the terminal position, whereby after passing the ratchet or securing elements these are moved back to their initial position either by an external spring or bending force stored in the element itself. The ratchet or securing element with positive locking then prevents the locking stud from moving against the movement direction from the initial position to the terminal position in the piston past the ratchet- or securing element to its initial position.
Positive locking is achieved particularly advantageously if the ratchet- or securing element is a contact stud, which fully passes through the window-type aperture, so that if the stud is moved with its free end in relation to the piston against the movement direction from the initial to terminal position, it is pressed by the stud against a stop. Only by destroying the ratchet or locking element can the piston now be moved back to its initial position. Through corresponding design of the ratchet or locking element however the force necessary for destruction can be calculated in such a way that destruction by forces acting on the piston from outside is not possible.
Advantageously the electrical detonator together with any necessary explosive is arranged directly in the cavity of the housing and therefore in the cylinder of the pneumatically operated cylinder. The electrical detonator has electrical ignition contacts, which are fed out from the cavity through at least one aperture, so that they can be connected to an ignition circuit. The housing of the pyrotechnic actuator is designed to advantage in such a way that in the unassembled condition of the pyrotechnic actuator the electrical connections of the detonator are short-circuited by means of a short-circuit element. This short-circuit element can be secured on the housing by means of a snap-connection; it is however also conceivable that the short-circuit element is injection moulded directly during manufacture of the housing especially made from plastic. If the housing is a metallic material, stud-shaped elements can be moulded in such a way that these short-circuit the electrical contacts when the detonator is inserted into the cavity. Irrespective of whether the short-circuit elements have been moulded or added afterwards, they are moved away, on connection to an electrical plug, which is designed to connect the detonator with the ignition electronics, from the electrical connections of the detonator, so that the short-circuit is broken.
An equally preferred embodiment is the case if in addition to the piston a part which can pivot and/or is displaceably held is arranged on or in the housing, is in communication with the piston and is swung or displaced when the piston moves from its initial to its terminal position. Through integration of such a pivotable part, which is especially designed as a rocker or lever, an unlocking or locking system can be realised with few components, whereby through the leverage effect any amount of leverage force or travel directions can be achieved with one and the same cylinder piston system. Such a pyrotechnic actuator can be used for example as an unlocking mechanism for conventional roll bar systems, where electromagnetic unlocking mechanisms have been used up till now. The pyrotechnic actuator can with its cylinder piston system replace conventional solenoids, which are not only heavy in regard to their deadweight, but are also complicated and expensive in regard to their structure. Through corresponding sealing of the cavity by the piston itself and the housing shape a darting flame or gas arising during the explosion does not escape from the piston, so that the pyrotechnic actuator works very gently and on the other hand cannot ignite flammable substances which may escape from a vehicle in the event of an accident. If with conventional electromagnetic unlocking systems for roll bars on vehicles the solenoid is secured to a housing, which seats the unlocking bar or lever, the cavity can be an integral part of the housing, as a result of which parts are saved to advantage and at the same time the system can be produced in few stages.
The pyrotechnic actuator can be used advantageously to release or move a roll-bar of a vehicle. In this case in an advantageous embodiment the roll-bar with its two ends and the parts inserted in these can interact with the cavity of the actuator housing, so that gas is produced by igniting the detonating capsules, which makes the roll-bar shoot out of its initial position. In the case of this application the piston should be rigidly attached to the roll bar. It is however also possible to operate the roll-bar by the piston via a gearbox. In this case it is possible to use a pyrotechnic actuator at each end of a roll-bar. It is also however conceivable that each end of an especially V- or U-shaped roll-bar interacts with a piston or forms this itself, whereby the pistons lie in cylinders, the working spaces of which are connected to each other via connection pipes, whereby a detonating capsule and a suitable explosive for the gas development are placed in the connecting pipe. As soon as the detonating capsule is ignited, gas arises in the feed pipes, which moves the pistons and with them the roll-bar with or without using a gearbox from the initial position to the terminal position. Through the explosion-type development of the quantity of gas the roll-bar is moved in a few milliseconds from the initial to the terminal position. By means of corresponding locking- and retention mechanisms, which can be arranged on the roll-bar itself, the roll-bar is securely retained in its terminal position.
It is naturally evident that the size of the pyrotechnic actuator can be larger or smaller depending on the type of use, so that the corresponding stroke of the piston or force needed to trigger the operation is achieved. It is equally conceivable that ratchet or retaining elements are provided which are moulded or secured on the piston or cylinder, which with the gas development are destroyed in particular broken off, so that the piston can reach its terminal position. The piston can then be retained in its terminal position by additional retaining elements, as soon as it has reached this position.
If the pyrotechnic actuator is used in such a way that the piston does not have to be retained in its terminal position, the corresponding locking mechanism to retain the piston in its terminal position can be dispensed with, as a result of which less material and parts are needed to make the pyrotechnic actuator.
It is clearly evident that the form of the cylinder and piston can be selected as required. If the cavity has to be cut in the housing in a subsequent machining operation, it is especially easy from the design aspect to select a circular form of the cylinder, as a result of which the cavity can be made by means of a pocket hole.
If the housing is made from a plastic, this can be reinforced by additional metal parts against the effects of outside mechanical forces. Equally the piston can be reinforced by additional reinforcing parts, which advantageously equally form the ratchet- and/or retaining elements.